1. Field of the Invention
This invention relates generally to fasteners and, more particularly, to fasteners that coact with a receiving hole in a panel to prevent rotation of the fastener relative to the panel.
2. Description of the Related Art
When fixtures are to be attached to panels, or panels are to be joined together, a mechanical attachment often is preferable to other means of attachment, such as adhesives. Mechanical attachment typically requires less surface preparation than adhesives, and many adhesives can be caustic. Moreover, a mechanical attachment generally can be removed and reinstalled. Mechanical attachment is typically accomplished using a threaded fastener system, such as screws threaded into the panels, or bolts used in combination with threaded fasteners, such as nuts. Sometimes, screws are not desirable or cannot be used. For example, a screw requires that the attachment hole in the panel be threaded, which is a more time-consuming operation than drilling a bolt hole. Some materials, such as composite panels constructed from fibers and hardened resin compounds, cannot be threaded due to their brittleness, and therefore cannot be used with screws.
A difficulty associated with using a bolt and fastener combination is that a fastener typically must be held in place relative to the panel when the bolt is being turned so that the fastener does not rotate as the bolt is being turned. If the fastener has a multi-sided body, then a receiving hole can be provided in the panel, having sides that complement the sides of the fastener body and that cooperate with the sides of the fastener to prevent rotation. The receiving hole in the panel, however, can be very difficult to prepare, especially in the case of brittle, composite panels. Some of these difficulties can be overcome by using fasteners such as plate nuts and press nuts.
A plate nut includes an internally threaded nut body having laterally projecting tabs on its bottom end. Each tab includes an attachment hole that can receive a bolt, rivet, or the like to attach the plate nut to a panel. The plate nut is attached to the panel by drilling three holes in the panel, one of which is aligned with the threaded bore of the nut body and the other two of which are aligned with the attachment holes of the tabs, and by bolting or riveting the plate nut to the panel through the attachment holes. A bolt then can be threaded into the nut body for attachment of a fixture or second panel without having to hold the nut in place during tightening of the bolt. Unfortunately, plate nuts require costly drilling and finishing steps, add weight to the finished assembly, and take up a greater amount of space.
A press nut includes a fastener body having an internally-threaded bore and an annular attachment flange at its bottom end, just below a circumferential groove. The panel to which the press nut is to be attached is prepared by drilling a single hole, larger than the internal bore of the press nut. A drive tool is used to press the nut into the panel and deform the panel material so that some of it flows into the circumferential groove against the flange and holds the nut in place. The press nut does not have to be held in place during tightening of the bolt, requires fewer preparation steps than a plate nut, and is lower in weight and size.
The press nut does have limitations, however. If the panel material is not sufficiently thick or hard, the press nut can pull through the panel as the bolt is being tightened. Because composite panels tend to be relatively brittle, the composite material does not readily flow into the circumferential groove of the press nut. Thus, press nuts are not ordinarily used with composite materials. Finally, it is possible for the torque applied to the bolt during tightening to be sufficient to rotate the press nut in the composite material, eliminating the advantage of one-handed operation.
From the discussion above, it should be apparent that there is a need for a threaded fastener system that prevents a fastener from rotating during installation, that does not require a complicated receiving hole, and that can be used in conjunction with composite panels without pulling through or otherwise damaging the panels. The present invention satisfies these needs.